Electric power supplied to a consumer such as a building from a power distribution grid may widely vary according to working conditions of electric power consuming devices (loads). So, in many cases, heavy consumers, such as industrial plants who consume great electric power, are equipped with local power supply systems each of which has a battery for in order to equalize (peak-cut-operation) the electric power supplied from the power distribution grid. This kind of power supply system stores electric power in the battery in a time zone, e.g., night, with comparatively little amount of electric power used, and supplies electric power from the battery in a time zone with comparatively much amount of electric power used. Since the maximum amount of electric power, i.e., peak amount, supplied from the power distribution grid may be suppressed by having the power supply system, the consumer may reduce payment, i.e., a contracted basic fee, for supplying electricity to a power supply company.
In general, an electric power converter, such as a DC/DC converter, is disposed between the battery and a power supply line connected with a load. The electric power converter adjusts voltage between the power supply line and the battery, and connects both. Electric power stored in the battery is boosted by the electric power converter, and then, supplied to the load through the power supply line.
It is known that an operating efficiency of the electric power converter may be the highest when it is operated to output the rated power. In other words, an operating efficiency of the electric power converter is lowered when outputting power lower than the rated power. Based on this, the power supply system disclosed in Patent Literature 1 is configured to estimate a time zone at which a power consumption of the consumer is kept continuously great, i.e., a time zone at which the electric power converter may continuously output the rated power, and to supply electric power from the power supply system at the estimated time zone. Since the electric power converter may be continuously operated at high efficiencies, it is possible to effectively output the storage electric power in the battery and supply it to the load.